1. Field of the Invention
This invention relates to an electron beam apparatus and also to an image-forming apparatus such as display apparatus that can be realized by using it.
2. Related Background Art
There have been known two types of electron-emitting device; the hot cathode type and the cold cathode type. Of these, the cold cathode type refers to devices including surface conduction electron-emitting devices, field emission type (hereinafter referred to as the FE type) devices and metal/insulation layer/metal type (hereinafter referred to as the MIM type) electron-emitting devices.
Examples of surface conduction electron-emitting device include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10, 1290, (1965) as well as those that will be described hereinafter.
A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. While Elinson proposes the use of SnO2 thin film for a device of this type, the use of Au thin film is proposed in [G. Dittmer: xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)] whereas the use of In2O3/SnO2 and that of carbon thin film are discussed respectively in [M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)] and [H. Araki et al.: xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)].
FIG. 19 of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell. In FIG. 19, reference numeral 3001 denotes a substrate. Reference numeral 3004 denotes an electroconductive thin film normally prepared by producing an H-shaped thin metal oxide film by means of sputtering, part of which eventually makes an electron-emitting region 3005 when it is subjected to an electrically energizing process referred to as xe2x80x9cenergization formingxe2x80x9d as will be described hereinafter. In FIG. 19, the thin horizontal area of the metal oxide film separating a pair of device electrodes has a length L of 0.5 to 1 [mm] and a width W of 0.1 [mm]. Note that, while the electron-emitting region 3005 has a rectangular form and is located at the middle of the electroconductive thin film 3004, there is no way to accurately know its location and contour.
For preparing surface conduction electron-emitting devices including those proposed by M. Hartwell et al., the electroconductive film 3004 is normally subjected to an electrically energizing process, which is referred to as xe2x80x9cenergization formingxe2x80x9d, to produce an electron-emitting region 3005. In the energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1V/min. is applied to given opposite ends of the electroconductive film 3004 to partly destroy, deform or transform the thin film and produce an electron-emitting region 3005 which is electrically highly resistive. Thus, the electron-emitting region 3005 is part of the electroconductive film 3004 that typically contains a gap or gaps therein so that electrons may be emitted from the gap. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting-region 3005 whenever an appropriate voltage is applied to the electroconductive film 3004 to make an electric current run through the device.
Examples of FE type device include those proposed by W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical Properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
FIG. 20 of the accompanying drawings illustrates in cross section a typical FE type device. Referring to FIG. 20, the device comprises a substrate 3010, an emitter wiring 3011, an emitter cone 3012, an insulation layer 3013 and a gate electrode 3014. When an appropriate voltage is applied between the emitter cone 3012 and the gate electrode 3014 of the device, the phenomenon of field emission appears at the top of the emitter cone 3012.
Apart from the multilayer structure of FIG. 20, an FE type device may also be realized by arranging an emitter and a gate electrode on a substrate substantially in parallel with the substrate.
MIM devices are disclosed in papers including C. A. Mead, xe2x80x9cOperation of tunnel-emission Devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961). FIG. 21 illustrates a typical MIM device in cross section. Referring to FIG. 21, the device comprises a substrate 3020, a lower metal electrode 3021, a thin insulation layer 3022 as thin as 100 angstroms and an upper electrode having a thickness between 80 and 300 angstroms. Electrons are emitted from the surface of the upper electrode 3023 when an appropriate voltage is applied between the upper electrode 3023 and the lower electrode 3021 of the MIM device.
Cold cathode devices as described above do not require any heating arrangement because, unlike hot cathode devices, they can emit electrons at low temperature. Hence, the cold cathode device is structurally by far simpler than the hot cathode device and can be made very small. If a large number of cold cathode devices are densely arranged on a substrate, the substrate is free from problems such as melting by heat. Additionally, while the hot cathode device takes a rather long response time because it operates only when heated by a heater, the cold cathode device starts operating very quickly. Therefore, studies have been and are currently being conducted on cold cathode devices.
For example, since a surface conduction electron-emitting device has a particularly simple structure and can be manufactured in a simple manner, a large number of such devices can advantageously be arranged on a large area without difficulty. As a matter of fact, a number of studies have been made to fully exploit this advantage of surface conduction electron-emitting devices. Studies that have been made to arrange a large number of devices and drive them effectively include the one described in Japanese Patent Application Laid-Open No. 64-31332 filed by the applicant of the present patent application.
Applications of surface conduction electron-emitting devices that are currently being studied include charged electron beam sources and electron beam apparatuses such as image displays and image recorders.
U.S. Pat. No. 5,066,883, Japanese Patent Application Laid-Open Nos. 2-257551 and 4-28137 also filed by the applicant of the present patent application disclose image display apparatuses realized by combining surface conduction electron-emitting devices and a fluorescent panel that emits light as it is irradiated with electron beams. An image display apparatus comprising surface conduction electron-emitting devices and a fluorescent panel can be highly advantageous relative to comparable conventional apparatuses such as liquid crystal image display apparatuses that have been popular in recent years because it is of a light emissive type and does not require a backlight to make it glow.
On the other hand, U.S. Pat. No. 4,904,895 of the applicant of the present patent application discloses an image display apparatuses realized by arranging a large number of FE-type devices. Other examples of image display apparatus comprising FE-type devices include the one reported by R. Meyer [R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, p.p 6-9 (1991)].
Japanese Patent Application Laid-Open No. 3-55738 also filed by the applicant of the present patent application describes an image display apparatus realized by arranging a large number of MIM-type devices.
Of the known image-forming apparatus comprising electron-emitting devices, those of a flat type are attracting attention and expected to replace display apparatus of the cathode ray tube type because they take little space and lightweight.
FIG. 22 is a schematic perspective view of a flat type image-forming apparatus, showing the inside by partly cutting away the display panel.
Referring to FIG. 22, there are shown a rear plate 3115, lateral walls 3116 and a face plate 3117. The envelope (airtight container) of the image-forming apparatus for maintaining the inside of the display panel in a vacuum state is formed by the rear plate 3115, the lateral walls 3116 and the face plate 3117.
A substrate 3111 is rigidly secured to the rear plate 3115 and a total of Nxc3x97M cold cathode devices 3112 are arranged on the substrate 3111 (where N and M represents natural numbers not smaller than 2 that may or may not be different from each other and will be selected appropriately depending on the number of pixels to be used for displaying an image). As shown in FIG. 22, the Nxc3x97M cold cathode devices are wired by M row directional wires 3113 and N column directional wires 3114. The unit comprised of the substrate 3111, the cold cathode devices 3112, the row directional wires 3113 and the column directional wires 3114 is referred to as multi-electron beam source. An insulation layer (not shown) is arranged for electric insulation between the row directional wires 3113 and the column directional wires 3114 at least at the crossings of the row directional wires 3113 and the column directional wires 3114.
A fluorescent film 3118 comprising fluorescent bodies (not shown) of the three primary colors of red (R), green (G) and blue (B) is arranged on the lower surface of the face plate 3117. Black members (not shown) are arranged to isolate each of the fluorescent bodies of the fluorescent film 3118 and a metal back 3119 typically made of Al is arranged on the side of the fluorescent film 3118 facing the rear plate 3115.
In FIG. 22, Dx1 through Dxm, Dy1 through Dyn and Hv represents respective electric terminals provided to electrically connect the display panel and an electric current (not shown) and having an airtight structure. The terminals Dx1 through Dxm are electrically connected to the row directional wires 3113 of the multi-electron beam source and the terminals Dy1 through Dyn are electrically connected to the column directional wires 3114 of the multi-electron beam source, whereas the terminal Hv is electrically connected to the metal back 3119.
The inside of the airtight container is held to a degree of vacuum of about 10xe2x88x926 Torr. As the display area of the image-forming apparatus increases, means will have to be provided to prevent the rear plate 3115 and the face plate 3117 against deformation and/or destruction due to the pressure difference between the inside and the outside of the air tight container. The use of a thick rear plate 3115 and a thick face plate 3116 is not feasible because it can increase the weight of the image-forming apparatus and the image displayed on the display panel can become distorted or be accompanied by a phenomenon of parallax if viewed askant. Thus, structural supports (that are referred to as spacers or ribs) 3120 that are made of a thin glass plate are arranged in the airtight container of FIG. 22 in order to make the rear plate 3115 and the face plate 3116 withstand the atmospheric pressure. The substrate 3111 carrying thereon a multi-electron beam source and the face plate 3116 carrying thereon a fluorescent film 3118 are then separated by a distance between a fraction of a millimeter and several millimeters and the inside of the airtight container is held to an enhanced degree of vacuum as described earlier.
As a voltage is applied to the cold cathode devices 3112 of an image-forming apparatus comprising a display panel as described above by way of the extra-container terminals Dx1 through Dxm and Dy1 through Dyn, each of the cold cathode devices emits electrons. Then, a high voltage between several hundred volts and several kilovolts is applied to the metal back 3119 by way of the extra-container terminal Hv to accelerate the emitted electrons and make them collide with the inner surface of the face plate 3117. As a result of this, the fluorescent bodies of the three primary colors of the fluorescent film 3118 are energized to emit light and display an image on the display panel.
Therefore, the object of the present invention is to provide an electron beam apparatus comprising members such as spacers that can be manufactured and used to facilitate suppression of electric discharges.
According to an aspect of the invention, the above object is achieved by providing an electron beam apparatus comprising an electron source having electron beam emitting devices, an electrode for controlling electrons emitted from the electron source and members arranged between the electron source and the electrode, wherein the members have a high resistance film on the surface and at least a low resistance layer on the side facing the electrode or the electron source and the high resistance film is electrically connected to either the electrode or the electron source by way of the low resistance layer, the low resistance layer being covered at least partly by the high resistance film. For the purpose of the invention, the members may include spacers for securing a distance between the electron source and the electrode.
Preferably, the low resistance layer is covered by the high resistance film in an boundary area held in connection with the high resistance film. Alternatively, the low resistance layer may be covered by the high resistance film in an area exposed to ambient air. Alternatively, the low resistance layer may be entirely covered by the high resistance film. Preferably, the members have the low resistance layer and the high resistance film sequentially formed in the mentioned order. Alternatively, the low resistance layer may be arranged on the end face of the members facing either the electrode or the electron source and extending to the lateral sides thereof and the extended portion of the low resistance layer is covered by the high resistance film at least at the extreme ends thereof. Alternatively, the high resistance film may be arranged to cover the low resistance layer at least on the end face facing the electrode or the electron source. Still alternatively, the low resistance layer may be covered by the high resistance film at least in part of the area exposed to ambient air.
For the purpose of the invention, a low resistance layer refers to a layer that substantially facilitates the movement of an electric charge from the high resistance film to the electron source or the control electrode (acceleration electrode) if compared with an arrangement that is devoid of such a low resistance layer. More specifically, the high resistance film shows a resistivity higher than the low resistance layer and/or the sheet resistance of the high resistance film is higher than that of the low resistance layer so that the movement of carriers from the high resistance film toward the electron source or the control electrode is facilitated.
According to another aspect of the invention, there is provided an electron beam apparatus comprising an electron source having electron beam emitting devices, an electrode separated from the electron source and members arranged between the electron source and the electrode, wherein the members have a film arranged on the surface and adapted to allow a minute electric current to flow therethrough and an end electrode arranged at least at the end facing the electron source or the electrode, the film covering at least part of the end electrode.
Preferably, the end electrode is covered by the film at least in the area connected to the film. Alternatively, the end electrode may be covered by the film in an area exposed to ambient air. Alternatively, the end electrode may be entirely covered by the film. Preferably, the members have the low resistance layer and the high resistance film sequentially formed in the mentioned order. Alternatively, the end electrode may be arranged on the end face of the members facing either the electrode or the electron source and extending to the lateral sides thereof and the extended portion of the low resistance layer is covered by the film at least at the extreme ends thereof. Alternatively, the high resistance film may be arranged to cover the low resistance layer at least on the end face facing the electrode or the electron source.
For the purpose of the invention, the film is preferably adapted to alleviate the electric charge produced by electrons striking the member. More specifically, the film is preferably adapted to allow a minute electric current to flow therethrough.
Preferably, the electron source has a plurality of electron emitting devices connected by wires and the members are electrically connected to the wires.
Preferably, the electron source has a plurality of electron emitting devices connected by a plurality of row directional wires and a plurality of column directional wires for a matrix wiring arrangement.
Preferably, the electrode is an acceleration electrode for accelerating electrons emitted from the electron source.
For the purpose of the invention, the electron emitting devices are cold cathode devices or surface conduction electron emitting devices.
According to a still another aspect of the invention, there is provided an image-forming apparatus comprising an electron beam apparatus and adapted to irradiate a target with electrons emitted from cold cathode devices according to an input signal to form an image. Preferably, the target is a fluorescent body.
If the low resistance layer is covered at least partly by the high resistance film, any electric discharge that may be caused by a concentrated electric field of the low resistance layer can be effectively prevented from taking place.
According to still another aspect of the invention, there is provided a method of manufacturing a member to be used in an electron beam apparatus having an electron source and an electrode separated from the electron source, the member being adapted to be arranged between the electron source and the electrode, the member having a low resistance layer arranged at least on the side facing the electrode or the electron source and a high resistance film electrically connected to the low resistance layer, the method comprising a step of forming the high resistance film to cover at least part of the low resistance layer.
Preferably, in the step of forming the high resistance film, the high resistance film is formed on the low resistance layer at least on the side facing the electrode or the electron source of the member and, at the same time, on the sides other than the side facing the electron source or the electrode to facilitate the manufacture of the member.
According to still another aspect of the invention, there is also provided a method of manufacturing a member to be used in an electron beam apparatus having an electron source and an electrode separated from the electron source, the member being adapted to be arranged between the electron source and the electrode, the member having an end electrode arranged at least on the side facing the electron source or the electrode and a film electrically connected to the end electrode, the method comprising a step of forming the film to cover at least part of the end electrode.
Preferably, in the step of forming the film, the film is formed at least on the side facing the electron source or the electrode and, at the same time, on the sides other than the side facing the electron source or the electrode to facilitate the manufacture of the member.